New technologies have made it possible to produce what are referred to as supercapacitors, which differ from conventional capacitors by having a high power density of, typically, 1–3 kWh/kg, a high cycling capability and a high degree of mechanical robustness. This opens up numerous options for use in the field of motor vehicle technology, and supercapacitors such as these may even be used as short-term stores for electrically powered vehicles.
In comparison to electrochemical energy stores, supercapacitors have the disadvantage of their relatively low energy content, which depends to a major extent on the output voltage of the supercapacitor. During operation in a standby mode, self-discharge also takes place, with the supercapacitor being slowly discharged through loads when the motor vehicle engine is switched off or through supercapacitor compensation circuits. When the output voltage falls below a specific limit, this can have a considerable adverse effect on the performance capability and on the behavior of the supercapacitor in the standby mode, or the capacitor may fail entirely.
Against this background, the object of the present invention was to provide voltage regulation in the electrical power supply system of a motor vehicle having a supercapacitor, which voltage regulation ensures that the supercapacitor has a long life and operates reliably in the standby mode.